The present invention relates to a dual coupling gear mechanism for a motor vehicle, having a first input shaft and a second input shaft and having a first and a second countershaft, the input shafts and the countershafts being connected to each other by means of a plurality of switchable wheel sets in order to establish at least seven forward gear stages and at least one reverse gear stage, at least one wheel set having a fixed wheel which is connected to one of the input shafts and two loose wheels which are rotatably supported on the first and on the second countershaft, respectively, and which are in engagement with the fixed wheel.
Dual coupling gear mechanisms are generally known in the prior art. They have two partial gear mechanisms of which one is associated with the even gear stages and the other is associated with the odd gear stages. To this end, dual coupling gear mechanisms have two input shafts which are connected to a dual coupling arrangement which has two friction couplings which can be controlled independently of each other (for example, wet-running multi-disc couplings or dry friction couplings). An input of the dual coupling arrangement is generally connected to a drive motor such as an internal combustion engine. By means of intersecting operation of the two friction couplings, gear changes can be carried out in a manner without traction interruptions.
Such dual coupling gear mechanisms may be arranged in a motor vehicle in the longitudinal direction or transversely relative to the longitudinal direction. In particular in the latter case, there is a great requirement for an axially short structural length. To this end, it is known to arrange two countershafts parallel with an input shaft arrangement, on which loose wheels can be distributed for engaging and disengaging gear stages. In this instance, output wheels of the countershaft are in engagement with an input member of a differential, which distributes drive power to two driven wheels of the motor vehicle.
Furthermore, a significant parameter in the construction of dual coupling gear mechanisms is the spread which generally correlates to the number of gear stages since the gear stages must, for example, be adapted to the characteristic of an internal combustion engine, since an appropriate stepping between the gear stages must be present. In the field of motor vehicle drive trains, there is also generally a requirement to hybridize the drive trains. This is generally intended to be understood to mean that, in addition to a drive motor in the form of an internal combustion engine, there is integrated in the drive train an electric engine which can be operated as a motor in order to provide alternative or additional drive power and/or can be operated in a recovering manner as a generator.
Finally, with such dual coupling gear mechanisms, there is generally to be provided a park locking arrangement which blocks the output of the drive train when a selection switch in the passenger space is in a P-position, that is to say, prevents the vehicle from rolling. Such parking locks may preferably be produced by means of park locking wheels which are securely connected to a shaft which acts directly on the driven wheels. The locking or the unlocking of the park locking arrangement may, for example, be carried out by means of a park locking detent.
In order to achieve an axially short structure, with the above-mentioned three-shaft gear mechanisms which have two countershafts, it is also known to implement a so-called “dual use”. With such a dual use, a fixed wheel of the input shaft arrangement is in engagement both with a loose wheel of the one countershaft and with a loose wheel of the other countershaft in order to thus be able to switch two gear stages alternatively by means of the one fixed wheel.
A dual coupling gear mechanism of the type mentioned in the introduction is known from document US 2010/0251840 A1, in which a park locking arrangement is arranged on a separate auxiliary shaft. Document DE 10 2004 056 936 A1 further discloses a similar gear mechanism, which has six forward gear stages. However, both gear mechanisms are not constructed for hybridization. The same applies to a seven gear mechanism which is known from document DE 103 05 241 A1.
Document WO 2006/040150 discloses another dual coupling gear mechanism which has six forward gear stages and a small spread. In this gear mechanism, an electric interior rotor engine is arranged parallel with the input shafts and can be connected by means of one or two clutches to one or two wheel sets of the gear mechanism. Electrical drive power can thereby be supplied to one or both partial gear mechanisms.
Document DE 10 2010 033 074 A1 further discloses a gear mechanism having a single starter coupling, which has two drive units and is constructed in such a manner that an electric engine can be used to support the traction force. The electric engine is connected to an input shaft and is arranged concentrically therewith so that significant limitations with respect to the assembly position of the electric engine are produced. The same applies to a dual coupling gear mechanism which is known from document DE 101 33 695 A1, which has six forward gear stages and which is constructed for a longitudinal assembly in the motor vehicle.
Document DE 10 2007 050 656 A1 discloses a dual coupling gear mechanism in which an electric engine is coupled to an input shaft of one of the partial gear mechanisms. A similar concept is known from document DE 10 2006 036 758 A1 in which an electric engine is securely coupled to the input shafts of the dual coupling gear mechanism, respectively.
A dual coupling gear mechanism with seven forward gear stages is further known from document DE 10 2010 020 856 A1, a park locking arrangement being arranged in this instance on a countershaft or a separate auxiliary shaft. In the first instance, a park locking wheel is orientated axially with respect to a loose wheel of the first forward gear stage. Hybridization is not mentioned in this document.
Finally, there is known from document DE 10 2004 049 832 A1 a dual coupling gear mechanism with seven forward gear stages for front transverse assembly, in which a plurality of toothed wheels of forward gear stages are used to establish a reverse gear stage so that a separate rotation direction reversal wheel is not necessary. However, a complex shift clutch which can connect two loose wheels to each other is required in this instance.
Against the above background, an object of the invention is to provide an improved dual coupling gear mechanism which is optimized with respect to the structural dimensions, in particular in an axial direction, with respect to the spread, with respect to the stepping, with respect to the hybridization and/or with respect to the parking lock implementation.